The present invention generally relates to a mechanical connection using non-circular inter-fitting components for transmitting torque. In particular to shaft/hub connection for transmitting torque.
In a typical machine construction, shaft/hub connections are used in may ways for transmitting torques between the shaft and hub. In addition to many requirements, the basic task of such types of connections is usually the transmission of high torques. For transferring such torque, the connections should be as compact and light as possible. In addition, it should be mountable without extensive installation and adjustment work. Dynamic loads are usually higher than static loads.
Since conventional shaft/hub connections usually don""t deal with an interference fit, only a certain portion of their contact surfaces truly participates in torque transmission. This causes high stresses in the components, which must be compensated for or reduced by an appropriately long connection. But the connection""s enlarged length again causes larger radial run-out and reinforces a relative motion between shaft and hub, during which no transmission of torque occurs (the so-called play). Enlargement of radial run-out also leads to undesired noises and vibrations. A longer connection moreover facilitates sliding of the surfaces upon each other, which again promotes the formation of fretting corrosion. Finally, these effects lead to a reduction in the lifetime of the shaft/hub connection and consequently that of the entire system.
DE 198 36 259 A1 shows a tight shaft/hub connection in which, to diminish or prevent the undesired play, a radial pressing device presses the hub toward the rotational axis in such a manner, that the hub""s inside contour engages the shaft free of play. The disadvantage of this embodiment is the need of additional components, which is associated with higher space requirements and costs.
Clamping-bush connections, in which a clamping-bush fits closely between the shaft and hub, are also a known means to reduce or prevent unwanted play. Such a clamping-bush demonstrates at least one element that enables the clamping-bush""s annular cross section to be enlarged, thereby pressing the clamping-bush against the shaft""s lateral surface on one side and against the hub boring""s inner surface on the other side, creating a connection free of play. DE 36 36 393 A1 describes clamping-bushes of such a type, in which positive locking is achieved by fitting both shaft and hub with longitudinal toothing, the clamping-bush being fitted with a matching toothing both on its inside and its outside. This embodiment too is associated with correspondingly higher costs and higher space requirements due to its extra components. More time and a consequently more cost-intensive work step is needed to assemble the clamping-bush.
Wedge-shaped elements, which are inserted between shaft and hub, are also well known. But these lead to an eccentricity of the shaft and therefore to point contacts or relatively small contact surfaces between shaft and hub. Therefore, there is a need in the industry to manufacture a shaft/hub connection that eliminates the above problems.
It is the objective of the present invention to create a mechanical connection with high functionality and lifetime for transmitting torque. It is yet another objective for the shaft/hub connection to be inexpensive to manufacture and easy to assemble.
The above objects are accomplished by having at least one of the components in the region of the slaving section, demonstrates at least two retaining sections angularly displaced to each other around the longitudinal axis.
The invention is based on the knowledge that a reduction of the play between shaft and hub can only diminish or neutralize high stresses in the component, fatigue, true running, and vibrations and only lead to the objective if the reduction of play occurs while there is a more centered position of the shaft in the hub. The inventors have discovered that longitudinal sections of one of the components, mutually displaced around their longitudinal axis and located in the region of the slaving section, ensure the shaft""s centricity within the hub, thereby achieving a more uniform transmission of torque. This can be achieved for example by torsion that extends across the entire length of the slaving section or also by two untorqued longitudinal sections that are connected to each other by a connecting section and mutually displaced therein. Several connecting sections, whose longitudinal sections are displaced against each other in steps or continuously, are also possible.
The reduction or neutralization of play in a centered shaft leads to a more favorable distribution of energy during torque transmission, thereby reducing stresses in the component, fatigue, true running, and vibrations. It is easy and quick to join, especially to thread, or to insert the connection together.
Continuous torsion permits the shaft to be inserted forward into the hub using an input cross section, the hub then turns because of the torsion as insertion becomes deeper and both the input and output cross sections come into contact with the hub. The terms input and output cross section are understood in terms of the shaft""s direction of insertion into the hub and refer to the opposite ends of the slaving section.
The shaft""s depth of insertion into the hub can be used both to reduce play by means of closely fitting (prestressing) the shaft on the hub and finally achieve a clamping action between shaft and hub. Transmission of torque in both directions free of play and change of direction free of play are consequently possible. Contact points or surfaces arise between the hub and shaft in all cases, at least in the regions of the shaft""s input and output cross sections. Due to the elasticity or plasticity of the material, intensified torsion before or during the transmission of torque can achieve a close fit along the entire length of the slaving section through deformation of the shaft and/or hub.
Moreover the degree of torsion can influence and determine different functions and parameters of the shaft/hub connection. A small degree of torsion, for example, means that stronger turning of the torqued component is necessary or possible until the desired effect, such as complete neutralization of play, has been attained. In contrast, torsion progressively running in the direction of the output cross section leads to easy insertion followed by increased turning of the shaft on an increasingly shorter segment. A diminishment or neutralization of play and a clamping action can be rapidly and easily achieved during assembly due to the short insertion distance. Degressive torsion in the direction of the delivery cross section is also conceivable for special applications. Mixed shapes, namely torqued components that can be changed (degressive, progressive, linear) across the length of the slaving section, are possible.
Polygonally shaped, especially trochoidally shaped cross sections of the shaft and hub have proven advantageous. A trochoid arises as the trajectory of a point as the point is carried along when a circle (moving circle) rolls along on or in a circle (rest circle). The number of and implementation of the trochoidal xe2x80x9cindentations and bulgesxe2x80x9d are variable. It has been shown that it is possible to transmit torque with minimum stress and, at the same time, with minimum relative motion between touching surfaces by using a trochoidal contour that has been optimized with respect to the number of xe2x80x9cindentations and bulgesxe2x80x9d and to their large and small diameters. Small differences in the contour of the touching components enable the properties of the shaft/hub connection to be changed, its lifetime and stability in particular.
The shaft/hub connection according to invention is particularly suited for use in automotive engineering, such as for the braking systems and wheel suspensions of motor vehicles. Here it is advantageous that a hub with polygonal inside contour according to invention doesn""t have to be broached. It is consequently unnecessary to manufacture it out of steel, the hub could be produced from cast iron for example. The shaft/hub connection according to invention is therefore also suitable in particular for use of this type, because brake systems for example are exposed to high thermal loading.
The invention shall be explained in more detail based on preferred embodiments illustrated in the drawing. It shows: